1. Field of the Invention
The present invention relates to a vehicle interior material, and more particularly to an impact absorbing member for vehicle interior suitably used for pillar garnish, roof side rail garnish, door waist garnish, etc., in an automobile.
2. Description of the Related Art
Polypropylene resins and rubber-enhanced styrene resins (ABS, AES, AAS) are widely used for the housings and components of home electric appliances, vehicle interiors and exteriors, etc., due to their superior impact-resistance, heat deform ability, and ease of molding.
On the other hand, vehicle interior materials include, as shown in FIG. 15, front pillar garnish 105F, center pillar garnish 101C and roof side rail garnish 101S that are respectively mounted to the vehicle interior side of the front pillar 105F, the center pillars 105C and roof side rails 105S. These vehicle interior materials are constructed not only in order to maintain the aesthetic appearance of the vehicle interior, but also to allow the impact received by a passenger from the vehicle body to be absorbed and reduced through plastic deformation at the area that comes into direct contact with a part of the passenger""s body (i.e., the head) during a collision of the vehicle, for example.
A typical conventional front pillar garnish 105F comprises, as described in Japanese Patent Application Laid-Open No. H9-175284, (i) a surface member 102 having an essentially C-shaped transverse cross-section, (ii) a panel-like vertical rib 103L that extends along the length of and along the rear surface of the surface member 102, and (iii) multiple panel-like horizontal ribs 103W that are essentially perpendicular to the vertical rib 103L and extend between the side walls of the surface member 102, as shown in FIG. 16 for example, and is fixed to the protrusion 107 of the inner panel comprising the front pillar 105F such that the ribs are in contact with the protrusion 107. In the event of a passenger collision, the impact is absorbed by the vertical rib 103L and the horizontal ribs 103W, which deform and become destroyed.
Incidentally, increased safety during vehicle collisions has been demanded in recent years in the United States. Impact absorption characteristics that meet a high safety standard in terms of HIC (head impact characteristic) provided by the FMVSS, a U.S. government agency, are demanded of molded products used in vehicle interiors or exteriors.
Various attempts have been made in order to meet this safety standard, as well as to maintain heat deformability and ease of molding, and the use of ABS resin using diene rubber and modified polypropylene as the molding materials has been proposed, but in any event, sufficient impact absorption characteristics have not yet been obtained.
In order to maintain a high level of impact absorption performance, the protrusion height of each rib must be large. Consequently, when the front pillar garnish 101F is mounted to the front pillar 105F, the front pillar garnish 101F projects out into the vehicle interior gap to a significant extent, giving rise to such problems that the passenger feels closed in, the field of view is narrowed, and the garnish poses an obstacle when the passenger enters and exits the vehicle.
In view of the problems identified above, an object of the present invention is to provide an impact absorbing member for vehicle interior that, while maintaining superior heat deformability, offers improved impact resistance that satisfies the above safety standard, reduces the protrusion height of the ribs, and reduces the degree to which the material projects into the vehicle interior space.
In order to attain these objects, the vehicle interior material pertaining to the present invention may be obtained by molding synthetic resin that has a tan xcex4 (loss tangent) peak height of 0.04 or higher and a peak temperature between xe2x88x9240 and 50xc2x0 C., as measured through viscoelasticity measurement. The impact absorbing member for vehicle interior of the present invention is suitable for use as a pillar garnish, roof side rail garnish or door waist garnish of an automobile.
The reason why the present invention has superior impact-resistance while maintaining heat deformability, and consequently can have a reduced rib protrusion height, will be explained below using pillar garnish as an example, based on the U.S. FMVSS201 standard.
First, the kinetic energy E0 (J) of a dummy head (virtual passenger""s head) is expressed by the following equation (1) based on the equation of motion.
E0=xc2xdmv2xe2x80x83xe2x80x83(1)
Here, m is the weight of the dummy head (4.6 kg), and v is the velocity (m/s) of the dummy head at the time of collision.
The dynamic energy W(J) absorbed by the deformation of the ribs is expressed by the following equation (2).
W=mxc2x7xcex1CONSTxc2x7Sxe2x80x83xe2x80x83(2)
Here, xcex1CONST is the average acceleration (m/s2) that is generated at the time of collision, and S is the amount of stroke (m).
Conventional vehicle interior materials are generally molded using a synthetic resin such as a polypropylene resin or a rubber-enhanced styrene resin (ABS, AES, AAS), and when the dummy head collides with the material, most of the kinetic energy E0 is absorbed through the structural deformation of the ribs, as described above. As a result, the equation (1) and the equation (2) are deemed equal, and the following equation (3) is obtained.
mxc2x7xcex1CONSTxc2x7S=E0xe2x80x83xe2x80x83(3)
As shown in FIG. 2(a), the dummy head""s kinetic energy E0 is efficiently absorbed by the deformation of the ribs, the HIC(d) requirement is met, and the stroke becomes the smallest when there is no curve gradient caused by a rising or falling rate of acceleration, and the acceleration in between is constant.
On the other hand, the head injury characteristic HIC(d) provided by the U.S. FMVSS201 standard is calculated based on the following equation (4).                                           (            4            )                    ⁢                      xe2x80x83                    ⁢                      HIC            ⁡                          (              d              )                                      =                              0.75446            xc3x97                                          (                                                      1                                                                  t                        2                                            -                                              t                        1                                                                              ⁢                                                            ∫                      t1                      t2                                        ⁢                                          α                      ⁢                                              ⅆ                        t                                                                                            )                            2.5                        xc3x97                          (                                                t                  2                                -                                  t                  1                                            )                                +          166.4                                    (        4        )            
If the following equations are substituted in the equation (4) and calculated, the following equation (5) is obtained.
xcex1=xcex1CONST/g
g=9.8 (m/s2) [gravitational acceleration]
t2xe2x88x92t1=V0/xcex1CONST
V0=6.67 (m/s) [15 mph (miles/h)]
xcex1CONST=(HIC(d)xe2x88x92166.4) /0.0167377)0.667xe2x80x83xe2x80x83(5)
Given that the HIC(d) level currently adopted as an internal standard by automobile manufacturers is 800 or less, and that the energy that can be absorbed by the distortion of the body panels (pillar outers, pillar inners, etc.) is approximately 100 in terms of HIC(d), the HIC(d) that should be substituted in the equation (5) when seeking the limit of the average acceleration is 900. If the average accelerate xcex1CONST is 1247.5 (ms2) or lower, the above standard is met.
If the equation (3) is calculated using this average acceleration xcex1CONST, the smallest value for the stroke amount S becomes 17.8 (mm), and therefore, it is seen that where a conventional vehicle interior material is concerned, the rib height must be 17.8 mm or more.
In addition, because the parts m and n that exist when the acceleration is rising and falling, respectively, are added, as shown in FIG. 2 (b), to the acceleration actually measured for the dummy head, the stroke amount S, i.e., the required rib height, increases further, resulting in an actual rib height of 18 to 19 mm or higher.
Incidentally, at the time of the collision of the dummy head, only a small part of the kinetic energy E0 is converted into loss energy such as heat energy. If the amount of this loss energy can be increased, the following equation (6) is obtained instead of the equation (3). It is therefore seen that by increasing the energy loss rate k, the average acceleration xcex1CONST to be absorbed via the deformation, destruction, etc. of the ribs decreases, and further, HIC(d) may be reduced. This equation (6) indicates, as shown in Table 1 below, that by increasing the energy loss rate k under a constant average acceleration xcex1CONST, the required stroke amount S is reduced, and the rib height may be further reduced.
mxc2x7xcex1CONSTxc2x7S=(1xe2x88x92k)E0xe2x80x83xe2x80x83(6)
k indicates the rate of energy loss.
Accordingly, as means for increasing this energy loss rate k, the present invention focuses on the tan xcex4 (loss tangent), as obtained via viscoelasticity measurement, of the synthetic resin from which the vehicle interior material is molded. It reduces HIC (d), or in other words, increases the impact resistance, and reduces the stroke amount of the ribs, making it thus possible to reduce the required rib height by increasing the peak height of this tan xcex4 to a value equal to or higher than 0.04 to promote micro-Brownian motion among the segments of the molded polymer material, thereby increasing the loss energy based on dynamic heat generation
It is preferred that the synthetic resin used to mold the impact absorbing member for vehicle interior of the present invention comprise a polypropylene resin, a rubber-enhanced styrene resin, a polycarbonate resin, a polyamide resin, a polyester resin or a polyphenylene ether resin, or an alloy resin combining these resins.
These resins have conventionally been used as vehicle interior materials, but their tan xcex4 in the test temperature range (19-26xc2x0 C.) defined by the U.S. standard FMVSS201 is around 0.02 to 0.03, and their loss energy due to heat generation is negligible.
In the present invention, by using these synthetic resins as the base resin, and by adding a norbornane polymer, a styrene-isoprene-styrene block copolymer, a hydrogen-added styrene-isoprene-styrene block copolymer, a styrene-isobutylene-styrene block copolymer, an isoprene-isobutylene copolymer, a chloroprene polymer, a (meth)acrylic ester resin, acrylonitryl-butadiene rubber, polyurethane, or silicone rubber, the tan xcex4 peak height of the synthetic resin is made 0.04 or higher, and the loss energy during passenger collision is increased.
The above synthetic resin preferably has superior heat deformability by which the HDT (heat deformation temperature) under a 1.82 MPa load becomes 70xc2x0 C. to 120xc2x0 C., and for the above alloy resin, an alloy resin comprising a polycarbonate resin and a rubber-enhanced styrene resin, an alloy resin comprising a polyamide resin and a rubber-enhanced styrene resin, or an alloy resin comprising a polyester resin, a polycarbonate resin and a rubber-enhanced styrene resin, is preferred.
The impact absorbing member for vehicle interior obtained by molding these synthetic resins comprises a surface member having an essentially C-shaped transverse cross-section, that is placed over the vehicle interior side of the vehicle panel with a gap in between, and multiple plate-shape ribs that protrude into the abovementioned gap from the rear surface of the surface member that faces the vehicle panel, and wherein each plate-shape rib is independent of the others and extends between the side walls of the surface member such that they are perpendicular to the length of the vehicle panel, and has deformation inducing means that, when impact is received from a passenger, causes the part that protrudes toward the vehicle panel to buckle in the middle part of the protrusion, such that during passenger collision, multi-stage deformation and destruction occur in which buckling and deformation begin in the middle part of the rib before the rib buckles along the protrusion base edge, providing efficient impact absorption in which an essentially constant acceleration is maintained as shown in FIGS. 2(a) and 2(b), and enabling the stroke amount due to the deceleration slope to be further reduced.
It is preferred that the surface member be placed over the panel protrusion of the vehicle panel that protrudes into the interior of the vehicle, that the protrusion edge of each plate-shape rib have a configuration such that it essentially travels along the protrusion surface and one of the passenger-side side faces continuing on neither side thereof,with these two surfaces comprising the above panel protrusion, and wherein the deformation inducing means includes at least one main notch that opens up at a position at which the protrusion edge faces the two-surface contact edge between the protrusion surface and one of the passenger surfaces of the panel protrusion, and comprises a total of two or more components selected from among notches, steps and thin areas formed on said protrusion edge. In a plate-shape rib constructed in this fashion, the buckling that occurs in the middle part of the protrusion is induced along virtual lines that connect the bottoms of the notches, the bottom edges of the steps or the bottoms of the thin areas, and these bottoms and bottom edges may become the points from which additional fissures occur toward the surface member. The generation and progress of these fissures, including fissures in the thin areas, contribute to more efficient impact absorption.
While the abovementioned surface member and plate-shape ribs are integrally molded, the vehicle interior material pertaining to the present invention is not limited to this implementation: A material in which the surface member and the plate-shape ribs are molded separately using any of the synthetic resins described above, and are assembled into one integral unit using a bonding means such as clips, thermal caulking, an adhesive agent or two-sided adhesive tape is also desirable.
An impact absorbing member for vehicle interior having this construction is suitably used as a front pillar garnish or center pillar garnish of an automobile in particular.